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Thorium, a predominant actinide in the Earth's crust, presents significant environmental and health risks due to its radioactive nature. These risks are particularly pronounced during the mining and processing of monazite for rare earth elements (REEs), which contain substantial thorium concentrations. Current instrumental analysis methods for thorium, offer high accuracy but require laborious sample preparations and expensive instruments, making them unsuitable for on‐site analysis. Herein, we present a class of color‐tunable luminescent lanthanide‐based metal–organic frameworks (Ln‐MOFs) as fluorochromic sensors for Th4+ cations. Utilizing a heterobimetallic Eu3+/Tb3+ doping strategy, the luminescence colors of EuxTb1‐x‐BDC‐OH can be finely tuned from red, to orange, and to green. More intriguingly, the higher Lewis acidity of Th4+ facilitates the transformation of EuxTb1‐x‐BDC‐OH into a UiO‐type Th‐MOF via a dissolution‐recrystallization mechanism. This process results in a gradual reduction of characteristic Ln3+ emissions and the emergence of blue color ligand‐based fluorescence, thereby leading to selective fluorochromic responses with increasing Th4+ concentrations and enabling visible detection of Th4+ cations. Additionally, a custom‐built portable optoelectronic device is fabricated, which directly converts luminescence colors into red‐green‐blue (RGB) values. This device enables easy quantification of Th4+ concentrations without the need for complex instrumentation. [ABSTRACT FROM AUTHOR]

Crystalline organic–inorganic hybrids, which exhibit colorimetric responses to ionizing radiation, have recently been recognized as promising alternatives to conventional X‐ray dosimeters. However, X‐ray‐responsive organic–inorganic hybrids are scarce and the strategy to fine‐tune their detection sensitivity remains elusive. Herein, an unprecedented mixed‐ligand strategy is reported to modulate the X‐ray detection efficacy of organic–inorganic hybrids. Deliberately blending the stimuli‐responsive terpyridine carboxylate ligand (tpc−) and the auxiliary pba− group with different ratios gives rise to two OD thorium‐bearing clusters (Th‐102 and Th‐103) and a 1D coordination polymer (Th‐104). Notably, distinct X‐ray sensitivity is evident as a function of molar ratio of the tpc− ligand, following the trend of Th‐102 > Th‐103 > Th‐104. Moreover, Th‐102, which is exclusively built from the tpc− ligands with the highest degree of π–π interactions, exhibits the most sensitive radiochromic and fluorochromic responses toward X‐ray with the lowest detection limit of 1.5 mGy. The study anticipates that this mixed‐ligand strategy will be a versatile approach to tune the X‐ray sensing efficacy of organic–inorganic hybrids. [ABSTRACT FROM AUTHOR]

A novel radio-photoluminescence material featuring fluorochromic responses toward UV or X-ray irradiation has been obtained. Such a unique monomer- to excimer-based luminescence transition allows for dosimetry of ionizing radiation in a ratiometric manner. Rather than quenching the luminescence, the radiation-induced radical species of Th-105 boost the excimer emission, rendering it as a rare material possessing radical-excimers. [ABSTRACT FROM AUTHOR]

The dissolution– recrystallization of metal- organic frameworks ( MOFs) opens exciting possibilitiesfor fluorochromic detection of radionuclides. In their Research Article ( e202410453), Jian Lin et al. introduce a novel method for detecting Th4+ ions using a series of color- tunable luminescent lanthanide- based MOFs. The inherent instability of MOFs is leveraged to enable Th4+ detection through an unprecedented dissolution– recrystallization mechanism, transforming a perceived limitation into a valuable tool for fluorochromic sensing of radionuclides. [Extracted from the article]